Its possible that weak signal is the problem and not bad splitters, you stated that when you pull the splitter the problem stops, whats happening is you're quadrupling the signal to that receiver. If your signal is borderline small changes in weather conditions could effect your reception causing it to come and go leading you to believe you have bad splitters. Do you have four HDTVs needing signal or are you using one antenna for analog and digital? If so you may what to install a digital (UHF only) antenna for your HD tuner. I'm in the Detroit area and have installed hundreds of antennas for HD reception and I've used a pre-amp only a couple of times for installs way out of the city. I've found if you don't really need a pre-amp it makes the reception worse.